1. Field of the Invention
This invention pertains to a telecommunication antenna, particularly one used for base stations of cellular communication networks (including GSM and UMTs networks). Such an antenna is made up of radiating element network spaced slightly apart. The invention particularly pertains to the reflecting means with which this antenna is equipped.
2. Description of the Prior Art
A telecommunications antenna sends and receives radio waves over frequencies specific to a telecommunications system used by that antenna. Thus, an antenna intended for the UMTS system uses waves whose frequencies are within the range of 1710 to 2170 MHz. A base station comprises a network of antennas, and supplies each antenna with waves whose frequencies are within the range that the antenna uses. However, the distance between the antennas is short, and as a result, every antenna has an influence on the adjacent antenna.
The document U.S. Pat. No. 5,710,569 mentions the problem of minimizing the lateral radiation of an antenna, a source of interference with neighboring antennas, by modifying the width of the horizontal beam and improving the front-to-back ratio. This document describes an antenna comprising arrayed dipoles attached to the flat base of a reflector whose edges fold upward. Choke reflectors are disposed within the area between the dipole and the lateral upward fold of the reflector, which they are distinct from, in such a way as to serve as a screen on other side of the row of dipoles. These choke reflectors are made up of metal sheets folded into L shapes and attached to the flat base of the reflector supporting the dipoles. They may move in a horizontal direction, so that they move closer to or further from the dipole array, in order to modify the characteristics of the antenna.
The document EP-0 973 231 states its purposes as minimizing the lateral lobes of an antenna, which are a source of interference with adjacent lobes, and to obtain the characteristics of a bipolarization with just one antenna. This document also mentions the possibility of controlling the isolation by adjusting the positions of the choke reflectors. This document describes an antenna comprising radiating elements attached to the flat part of a reflector comprising downward-folding edges. Two choke reflectors which may move longitudinally are disposed along the radiating elements on the flat part of the reflector. Transversal choke reflectors, furthermore, are placed between the radiating elements, perpendicular to the lateral choke reflectors.
In these documents, the term “choke reflector” refers to simple angle pieces which form two parallel flat surfaces which surround the arrayed radiating elements as closely as possible. The purpose of these choke reflectors is to modify the beam width value of the antenna. The authors of these documents have sought after a way to control the rated beam width value of the antenna by disposing the choke reflectors within the central area of the antenna, as close as possible to the dipoles.